Monday, June 27, 2011

Shakes on a Plane: Can Turbulence Kill You?

Image Credit: Jason Pratt

See that plane on the upper left?

Airplanes are scary. This indisputable fact originally came to my attention somewhere during college, when my relationship with flying matured from irritated ambivalence to full-blown phobic terror. There is something profoundly disturbing about being suspended thousands of feet in the air in a metal tube piloted by someone you’ve never even met. When I explain this to people who aren’t bothered by air travel, they foolishly try to persuade me with statistics about how flying is safer than driving blah, blah, blah…as though irrational fears could be soothed by something as banal as data.* Really, the only way to take my mind off my impending death is to pretend I’m not in an airplane at all. Distractions like food and music and in-flight magazine crossword puzzles go a long way toward accomplishing this, but all their hard work is undone the instant the plane encounters even a little turbulence. Turbulence has a way of snapping you back into the present moment, its every lurch and bump an unwelcome reminder that you’re hurtling through the stratosphere at over 500 miles per hour.

...this is what I think of every time I look at it.

My spring vacation† involved a total of 7 flights and amounted to something like 25 hours of time in the scary skies. Mercifully, every flight was smooth and trouble free, except for the very last one – a short jaunt from Dallas to Austin. I could tell the final phase of the trip was going to be less compliant than the previous portions. Thick clouds hung over the airport while we waited to board the plane. As soon as we were in the air, the pilots announced that there would be no beverage service due to some rough weather ahead. Throughout the next terrifying 40 minutes or so, we received various ominous announcements from the cockpit as the plane shuddered in increasingly malevolent winds, “We’re going to fly low today and try to stay below this storm,” and “Okay, so still pretty bumpy even at this altitude, but we should hopefully be there soon” etc. After we were safely back on the ground, I apologized to my boyfriend for all my in-flight whimpering, calling upon the mantra I’d heard dozens of times, “I know it’s just turbulence and it can’t hurt the plane, but it really feels like you’re about to crash.” But instead of laughing at me for being such a sissy, he launched into a lengthy discussion of how severe turbulence can cause plane crashes, and how the turbulence we’d just experienced had been pretty rough, and something about “wind shear” being capable of tearing planes in half.‡ I was really glad he didn’t share any of this with me during the flight.

Say It Isn’t So

Since anecdotal boyfriend babble is not always accepted as a reliable source, I’ve done some research on the question of whether turbulence can cause aviation disasters. The answer turns out to be a heavily-caveated yes. Turbulence can lead to plane crashes, but it is exceedingly rare. By some estimates, turbulence takes down about one plane per decade.§ This chaotic air movement - and its effects on the movement of the aircraft - is classified in degrees of light, moderate, severe and EXTREME (emphasis added by author). There’s also something called “chop” which is a more rhythmic bumpity-bumpity effect that comes in light and moderate flavors. Passenger perception of turbulence tends to be direr than that of experienced crew, so if you think you’ve been on the worst flight of your life, it’s likely you only witnessed moderate turbulence.

The good news is that airplanes are designed to withstand extreme turbulence (as well as lightning). The bad news is that, like all machines, airplanes age. Wear and tear that is no problem under normal circumstances can make aircraft less resilient to ridiculous levels of turbulence. Additionally, flying a plane that is being pummeled by rogue air masses isn’t the easiest thing in the world. Planes can be pretty much out of control during these episodes and, while temporary, the pressure is really on the pilot to react (but not overreact) in a way that keeps the aircraft from flying into the side of a mountain. If you think this all sounds melodramatic, consider a 1966 incident in which a BOAC (now British Airways) Boeing 707, flying near Mt Fuji, broke up in midair and crashed amidst harsh winds.

Your Wake, My Funeral

As frightening as that is, you should probably be more concerned about something called “wake turbulence”. Unlike turbulence created by naturally occurring differences in air flow (bad weather, pressure variations near mountains, jet streams, etc.), wake turbulence is caused by other airplanes, sort of like the wake created by a boat, except with air and much scarier. The worst part of wake turbulence is the creation of “wingtip vortices”, tornadoes of bumpy air generated by a plane’s wings that can take several minutes to dissipate.

Image Credit: NASA Langley Research Center

As with boat wake, this form of turbulence is not a problem for the planes creating it, but rather for the planes near it. Airports enforce strict limits regarding how much time must pass in between take-offs and landings to prevent one plane from getting caught in another’s wake. However, airports are increasingly crowded places with limited runway resources. Since they are travelling at slower speeds and pitched at awkward angles, planes that are taking off or landing are more vulnerable to turbulence. And, unfortunately, take off and landing are exactly the times when planes fly closest to one another.

As with other forms of turbulence, wake turbulence is more of a threat to small planes (especially when caused by the significant wakes of large commercial jets). Probably the largest aircraft to crash as a result of the phenomenon was a McDonnell Douglas DC-9 that got caught in the wake of a Lockheed L-1011 in 1972, prior to the implementation of the above-mentioned spacing regulations.** Wake turbulence allegedly also contributed to the 2001 demise of American Airlines Flight 587, though this crash is officially attributed to pilot error in response to the wake.

Reality Check

And now let me stress how very, very rare these occurrences are. Finding examples with which to freak you out was no easy task. Really, the biggest of your worries in the realm of bumpy air is encountering clear air turbulence (CAT) when you don’t have your seatbelt fastened. This is the surprise turbulence that occurs on a sunny day in seemingly smooth skies. The major impact of turbulence is not the causing of plane crashes, but rather bodily injury from all that jerking around. Every year, dozens of un-seatbelted passengers are seriously injured (and occasionally even killed) from being thrown around the cabins of twitchy planes. Your pilot isn’t just being an overbearing nag when he (or she) asks you to keep your seatbelt fastened when you aren’t walking around the cabin. CAT can come out of nowhere and knock the #%$ out of a plane. So buckle up, people.

* By the way, I’m afraid of cars too, making such logic even more useless to me.

† I went to Spain. It was lovely, thanks for asking.

‡ Wind shear turns out to be variations in speed and direction of air movement, which often leads to turbulence. Possibly he was talking about wake turbulence rather than wind shear. Maybe he even said wake turbulence. I don’t know, I was still a bit rattled (pun not intended, but permitted) at the time.

§ This was reported in the Guardian (via the aviation consultant Ascend) and they didn’t elaborate on what types of planes – or types of turbulence for that matter –were involved in these disasters.

** The DC-9 is still relatively small compared to a wide-body behemoth like the Lockheed L-1011.

7 comments:

Airplanes are very, very, very scary. I took my last flight 25 years ago. There was a problem in flight, which was resolved safely, but it scared me so badly I had to take the bus home (overnight) because I couldn't get on the return flight.

Nice piece. I could read it without shuddering only because I'll never fly again.

Nice post, I'm here because I was interested about the difference between the plane shaking caused by air turbulence and, having seen air crash investigation programs apparently it can be caused by the aircraft flying to slow or about to stall. I recently went on holiday to kos Greece where we where making our decent to land. It was a night flight and it looked clear outside where you could see the lights from various islands that we flew over. I hate that moment where the engines go quiet and you can hear the flaps lower because the plane nose drops and the angle feels really awkward, sometimss you get a roll in your stomach like going over the brow of a hill, it doesn't feel natural at all. The lights in the cabin where lowered as per procedure, most people where asleep and all of a sudden the plane started the shake a little, it didn't feel like a random bit of air turbulence, it felt more controlled and constant, it only lasted about 10 seconds but it was enough to make me think that we where flying far to slow and that's when I thought we would fall out of the sky. Whilst I'm not normaly anxious, I'm still convinced this wasn't turbulence and indeed we may have been flying to slow. The landing wasn't great either when the pilot made a few last minute corrections presumably caused by cross winds and we bounced on the runway twice but thankfully landed safely. It was no doubt a normal landing to the experienced pilot and cabin crew but honestly, I'm not sure I want to fly again after this. Think its a good idea to stop watching the flight investigation programmes as well. Could anybody confirm if indeed the planes do vibrate when flying to slow? Note - sent via smartphone so apologies in advance for spelling and grammar.